The invention is based on a fuel injection pump for internal combustion engines. In a fuel injection pump known from German Offenlegungsschrift No. 32 13 724, the pump piston has as its relief conduit an axial blind bore originating at the pump work chamber, from which bore a transverse conduit branches off to two first outlet openings. A radial conduit also branches off to a second outlet opening. This second outlet opening is offset with respect to the first outlet openings toward the pump drive side and cooperates with a radial bore, which is disposed in the annular slide and by way of which, serving as a conduit, a communication with the relief chamber can be established. In the known fuel injection pump the radial bore is disposed such that, at an annular slide position corresponding to the low-load operating range during the pump piston supply stroke, the second outlet opening is in communication with the radial bore, while in the full-load range, the second outlet opening does not come to communicate with the radial bore. This apparatus serves to allow only some of the supply strokes of the pump piston to be effective in the low-load range; accordingly, a plurality of radial bores are provided, distributed around the annular slide, so that only every other pump piston supply stroke, for instance, leads to a pressure buildup in the pump work chamber and hence to the injection of fuel. Correspondingly, only half of the cylinders of the internal combustion engine serve to drive the engine. This provision is meant to lower fuel consumption in the partial-load range.
A fuel injection pump of this type is also known from German Offenlegungsschrift No. 32 18 275, in which instead of the radial bores in the annular slide provided in the above-described known fuel injection pump, diametrically extending grooves originating at the end face of the annular slide are provided, which now, and together with the face end of the annular slide serving as a first control edge, cooperate with only a single outlet opening of the relief conduit. Thus the grooves have the second control edges for controlling the communication between the pump work chamber and the relief chamber prior to the coming into play of the first control edge. The annular slide here is not only axially displaceable on the pump piston as a function of the adjustment of a fuel injection quantity regulator, but is also rotatable by a torque device. By means of rotation, during the supply stroke of the pump piston, the outlet opening can be made to come into communication with one of the diametrically extending grooves in alternation, upon every supply stroke, or every other supply stroke, of the pump piston, depending on the number of grooves provided. Thus either the number of injections can be reduced by half, for example, similarly to what is known from the prior art described initially above, or the high-pressure supply of the fuel injection pump can be suppressed entirely. Furthermore, by reducing the width of the grooves, it is possible merely to throttle the outflow of fuel during a particular supply stroke, in order to reduce the fuel injection rate in the lower rpm range.
The quite-idle device that is thus realized has the effect that the engine can be operated while idling, for instance, with less combustion noise. For rotating the annular side, the known torque device is coupled rigidly to a crank, which is rotated during engine idling to cut off individual cylinders.